Odor Modeling: Cost-Effective Risk Management in the Face of Change

“Odor complaints continue despite action on many fronts.”“Eeew!”“Odour complaints are continuing. The measures the company has taken are not working,”Search the internet and these types of headlines are not hard to find. And it's more than community good will at stake, fines can go as high as $25,000 a day for odor violations in some areas, and quick fixes and band aid approaches are rarely effective. Unfortunately, the same nose that can smell odors, is not the best tool to identify problem sources, especially for facilities like wastewater treatment facilities, where there are a number of different odorous processes which have not only significantly different odor characteristics and intensities, but different potential for traveling offsite and into the surrounding community, due to source parameters such as distance to the fenceline, source height above ground, and exhaust velocity, as well as characteristics of the local climate and wind conditions. A much more effective approach to dealing with the uncertainty usually associated with odor complaints from complex sources, identifying the problem sources, and assisting in the design of cost-effective mitigation is through the use of odor modeling. This paper discusses the use of odor modeling at two wastewater treatment facilities as a strategic tool in planning and risk management. One facility is a medium-sized suburban facility that has been the subject of continuous and numerous odor complaints from the surrounding community. The second facility is a small wastewater treatment process located in the center of a major city and surrounded by tall residential apartment houses and sensitive receptors. The operator of this facility is looking to upgrade the odor control system with a less expensive but more effective technology. In both cases, it was critical to manage the risks. Failing to correctly identify and mitigate the problem sources at the mid-sized plant would further alienate the community and risk fines and potential litigation. Proposing a new but ineffective technology and odor control design at the center city facility would result in significant financial risk. A strategy that applies refined and targeted odor modeling to correctly identify the problem sources and assist in the scientific design of new systems to control odors reduces these risks. The paper also discusses some new and important changes associated with odor modeling, including a new format for the meteorological data that can lead to higher (but more realistic) impacts, and revised algorithms that can result in downwash impacts for even taller stacks. Consideration of these changes is important for odor sources that have had to demonstrate compliance with odor standards for environmental review or permitting in the past since re-evaluation might lead to significantly higher results.